Biopromotores de crescimento em Brachiaria brizantha cv. BRS Piatã: seleção, aspectos morfofisiológicos, anatômicos e bioquímicos

Abstract

The inoculation of beneficial microorganisms in forage grasses is a potentially advantageous technique for sustainable pasture management by decreasing the need for chemical fertilization to maintain pasture productivity and reclaim degraded pastures, under both conventional and integrated systems (i.e., subjected to shade). The aim of this study was to determine the most effective method of microorganism inoculation on Brachiaria (Syn. Urochloa) brizantha cv. BRS Piată, by examining its effect on selected morphological, anatomical, physiological, biochemical and qualitative traits. In addition, we examined the impact of inoculation on the growth characteristics of this forage grass cultivar, grown under contrasting light conditions. Screening tests were carried out in vivo, for three methods of inoculation: in the seed, seed and soil, and soil. The experiment was conducted in a greenhouse, under full sun and shade at the Federal Rural University of Amazonia (UFRA) (01°27'25 "S, 48°26'36" W) in Belém, Pará, Brazil. Pseudomonas fluorescens (BRM-32111) and Burkhoderia pyrrocinia (BRM-32113), when co-inoculated by soil drenching, modified the anatomy (leaf, stem, root), increased the photosynthetic rate (14%), water use efficiency (22%), Spad index (37%), chlorophyll (122%), nitrate (100%), proteins (80%), total carbohydrates (29%), starch (133%), N (30%), Р (20%), Mg (20%) and Fe (180%) contents and increased forage quality and biomass production of B.brizantha cv. BRS Piată. Co-inoculation promoted growth of B. brizantha under contrasting light conditions, increasing biomass production by more than 100% relative to unfertilized- and fertilized-control (non-inoculated) plants. Our results imply that the method of inoculation and the light environment are important in determining the potential of microorganism for promoting plant growth. This study attests that co-inoculation of P. fluorescens and B. pyrrocinia are effective biofertilizers to increase B. brizantha productivity and forage quality under full sun and shaded environments.